1. Field of the Invention
The present invention relates to an improved component for a plasma processing system and, more particularly, to an optical window deposition shield employed in a plasma processing system to provide optical access to a process space through the deposition shield.
2. Discussion of the Background
The fabrication of integrated circuits (IC) in the semiconductor industry typically employs plasma to create and assist surface chemistry within a plasma reactor necessary to remove material from and deposit material to a substrate. In general, plasma is formed with the plasma reactor under vacuum conditions by heating electrons to energies sufficient to sustain ionizing collisions with a supplied process gas. Moreover, the heated electrons can have energy sufficient to sustain dissociative collisions and, therefore, a specific set of gasses under predetermined conditions (e.g. chamber pressure, gas flow rate etc.) are chosen to produce a population of charged species and chemically reactive species suitable to the particular process being performed within the chamber (e.g. etching processes where materials are removed from the substrate or deposition where materials are added to the substrate).
Although the formation of a population of charged species (ions, etc.) and chemically reactive species is necessary for performing the function of the plasma processing system (i.e. material etch, material deposition, etc.) at the substrate surface, other component surfaces on the interior of the plasma processing chamber are exposed to the physically and chemically active plasma and, in time, can erode or become coated with deposits. The erosion or coating of exposed components in the plasma processing system can lead to a gradual degradation of the plasma processing performance and ultimately to complete failure of the system.
Thus, in order to minimize the damage of components of a plasma processing system, more particularly optical windows, an optical window deposition shield is mounted between the optical window and the plasma. FIG. 6 is a partial cross-sectional view of a conventional optical window deposition shield in relation to a chamber wall deposition shield. As seen in this figure, the optical window deposition shield 1 includes a main body 3 and a peripheral flange 5 used to connect the optical window deposition shield 1 with a chamber wall shield 10. As seen in the partial cross-section portion of the optical window deposition shield 1 itself, the optical window deposition shield 1, typically fabricated from aluminum, includes many high aspect ratio holes 7 that open to the plasma. The high aspect ratio holes 7 have a ratio of length to diameter of four or greater. While these high aspect ratio holes 7 allow viewing through the optical window deposition shield 1, because of their geometry, the high aspect ratio holes 7 do not allow plasma to form close to the optical window of a plasma chamber that the shield is used in. Further, the optical window deposition shield 1 can be coated with various protective materials. For example, the optical window deposition shield 1 can be anodized to produce a surface layer of aluminum oxide, which is more resistant to the plasma. Details of an optical window deposition shield in relation to a plasma processing chamber will be discussed with respect to FIG. 1 below.
While effective in shielding the optical window of a processing chamber, prior art optical window deposition shields such as the one shown in FIG. 6 pose problems. First, the process of forming multiple holes in a block of aluminum does not provide a large ratio of viewing area (i.e., holes) to metal region, thereby making viewing of the plasma properties through the shield 1 difficult.
Moreover, the prior art optical viewing window shields are expensive to manufacture and are typically machined to a specific shape corresponding to the chamber liner configuration. Therefore, periodic maintenance, such as removal of the optical window deposition shield 1 for cleaning and inspection, is performed to prolong the life of the shield. Because the optical window deposition shield 1 is an integral structure fastened to the chamber liner 10, removal is complicated and time consuming, which results in further expense in the way of labor and chamber down-time. Finally, the optical window deposition shield 1 is heavy and bulky making safe disposal difficult.
As an alternative to the optical window deposition shield, the damage of the optical window can be minimized by providing gas flow over the optical window to keep it free of plasma contact during plasma processing. However, the necessary gas flow device is expensive and cannot easily be retrofitted to an existing chamber.